Borosilicate glass (sometimes also called by the commercial name of Pyrex) is a stout material, known for its qualities of temperature jumps resistance and for its low dilation coefficient. It's produced through sobstitution of alkaline oxides because of the boron oxide in the vitreous network of silica, obteining this way a glass of smaller expansion. When the boron oxide goes into the silica network, it weakens its structure (because of the presence of planar boron atoms at three coordinates) and prominently lowers its softening point.